With a shift toward a multichannel due to the spread of a CATV (cable television) or the like corresponding to one form of cable television services, there has recently been an increasing demand for simultaneously reproducing a plurality of video and audio data from one video/audio data recording and reproducing device as distinct from a conventional VTR (Video Tape Recorder).
In order to meet this demand, a device (AV server) for recording and reproducing or playing back video and audio data by using a plurality of random accessible recording and reproducing media such as a hard disk, etc. is becoming pervasive.
The continuity of data is of importance to this type of device as distinct from a data recording and reproducing device for a computer. That is, if video and audio data necessary within a predetermined time cannot be recorded and played back, then images and voices are intermitted, so that the present device cannot be used as a moving picture/audio recording and reproducing device. Thus, even in the event that a malfunction occurs in a hard disk during recording, it is necessary to continuously receive and record transferred data and sequentially reproduce and transfer data without any delay when a reproduction request is issued.
Further, the shortening of a recovery time at the occurrence of a failure is one performance important to an AV server or the like. An increase in data transfer rate and the provision of a mass-storage hard disk capable of recording data for a long time are mentioned to meet a request for high picture quality and high sound quality.
Therefore, a device has been proposed wherein a plurality of hard disks are operated in parallel to speed up a transfer rate and even in the event of a failure in any hard disk, its reliability can be ensured by recording parity data therein.
FIG. 8 is a diagram showing a configuration of a disk array device provided with such hard disks. As shown in FIG. 8, a bus interface 1 is electrically connected to a data bus 3 so as to input and output record/playback data. A disk array controller 2 is electrically connected to the bus interface 1. Further, five hard disks H1 through H5 for providing disk array form are electrically connected to the disk array controller 2 in the present example.
The input recording data is distributed to and recorded on the hard disks H1 through H4 by the disk array controller 2. Parity data with respect to a plurality of data distributed simultaneously with this and simultaneously recorded are recorded on the dedicated hard disk H5.
When any hard disk fails, such a device can rebuild data by re-computing original data from the left-behind data. Since the missed record data can be recovered owing to its rebuilding, the disk array device can improve the reliability thereof even when it is applied to the aforementioned video/audio data recording and reproducing device.
Further, the parallel operation of the plurality of hard disks H1 through H5 allows an improvement in the transfer rate of input/output data. Thus, a video/audio data recording and reproducing device requiring a high-speed transfer rate which was impossible under the use of a single hard disk, can be configured by using the hard disks H1 through H5 provided in a disk array configuration in a recording and reproducing unit.
FIG. 9 is a conceptional view showing a data recording format on a hard disk H1. As shown in FIG. 9, pieces of data are placed on the disk in concentric-circle form or spiral form. One concentric circle called "track" is divided into data recording sectors each having a suitable size (normally 512 bytes) in the peripheral direction thereof. In the present example, a track 4 is divided into data recording sectors a through g and a spare sector h.
Several tracks 4 are normally integrated into one called "zone". In general hard disks, a structure is adopted which stacks a plurality of disks on one another and rotates the stacked one by one spindle motor. Tracks 4 on each disk, which are located at the same positions in the radial direction thereof, are collectively put into one called "cylinder". The spare sector h is disposed and managed for each zone or cylinder. Only one spare sector h is assigned to one track 4 on one disk in the present example.
FIG. 10 shows a state of a normally-recorded track 4. If no problem occurs in all the data recording sectors a through g upon recording and reproduction, then data DATA1 through DATA7 are normally recorded on the recording sectors a through g as shown in FIG. 10.
FIG. 11 illustrates a state of a track 4' at the time that data are relocated when a write error has occurred. When a malfunction occurs in a data recording sector c upon recording, for example, data is recorded on a spare sector h as shown in FIG. 11. The normally unrecordable and unreproducible data recording sector c results in a defective sector. In the defective sector, a logical address indicative of its position is assigned to the spare sector h. Thereafter, when a logical address for the data recording sector c is designated upon playback, the data on the spare sector h is read. Thus, the reliability of the entire device is improved.
However, in the video/audio data recording and reproducing device provided with the conventional disk array device, when the data recording sector c of the hard disk H3 shown in FIG. 8 is detected as being a defective sector as shown in FIG. 11, for example, the hard disk H3 cannot accept new data therein until a relocating operation (recovering operation) for recording DATA3 on a spare sector h is completed.
Thus, the video/audio data recording and reproducing device requiring the high-speed transfer rate spends time necessary for the relocating operation and thereby misses timing for recording DATA4, DATA5 or the like to be recorded subsequently to the data recording sector c. As a result, data to be recorded on data recording sectors d and e are missed and reproduced data cannot be transferred from the data recording sectors d and e at the request of reproduction.
Therefore, there may be often cases in which the conventional device handles such a problem by constructing the entire device in double form to thereby take a backup measure, or discontinuing working when a malfunction occurs and performing its retrial or preparing a mass-storage memory and temporarily saving data.
Even in this case, however, the device has no choice but to stop the recording and reproducing operations in the course of it. As a result, the continuous recording and reproducing operations cannot be effected on video/audio data. A problem arises in that the loss of such data will lead to a reduction in the reliability of the CATV system.
Therefore, the present invention provides a recording and reproducing device which allows a controller prepared within the device itself to automatically correct a write error of a hard disk, which occurs upon writing, within a time slot, thereby making it possible to continue recording and reproducing operations without loss of continuity for the request of recording and reproduction of video/audio data.